Jens Alfke created COUCHDB-1521:
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Summary: multipart parser gets multiple attachments mixed up
Key: COUCHDB-1521
URL: https://issues.apache.org/jira/browse/COUCHDB-1521
Project: CouchDB
Issue Type: Bug
Components: HTTP Interface
Affects Versions: 1.2
Reporter: Jens Alfke
When receiving a document PUT in multipart format, CouchDB gets the attachments
and MIME parts mixed up. Instead of looking at the headers of a MIME part to
identify which attachment it is (most likely by using the 'filename' property
of the 'Content-Disposition:' header), it processes the attachments according
to the order in which their metadata objects appear in the JSON body's
'_attachments:' object.
The problem with this is that JSON objects (dictionaries) are _not_ ordered
collections. I know that Erlang's implementation of them (as linked lists of
key/value pairs) happens to be ordered, and I think some JavaScript
implementations have the side effect of preserving order; but in many languages
these are implemented as hash tables and genuinely unordered.
This means that when a program written in such a language converts a native
object to JSON, it has no control over (and probably no knowledge of) the order
in which the keys of the JSON object are written out. This makes it impossible
to then write the attachments in the same order.
The only workaround seems to be for the program to implement its own custom
JSON encoder just so that it can write object keys in a known order (probably
sorted), which then enables it to write the attachment bodies in the same order.
NOTE: This is the flip side of COUCHDB-1368 which I filed last year; that bug
has to do with the same ordering issue when CouchDB _generates_ multipart
responses (and presents similar problems for clients not written in Erlang.)
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